Exploring the effect of oxygen environment on the Mo/CdTe/CdSe solar cell substrate configuration

Incorporating Se element into Cadmium telluride (CdTe)-based superstrate configuration solar cells have advanced impressively. However, molybdenum (Mo)/CdTe/CdSe substrate configuration devices remain relatively unexplored, and Mo foil oxidation behavior during the fabrication process is kept in the dark. This work investigates a fresh CdTe/CdSe substrate configuration solar cell using Mo substrates. Mo/CdTe/CdSe/ZnO/AZO/ITO solar cells have been fabricated, CdTe absorber layer was obtained by closed space sublimation (CSS) under ∼2000 pa pressure in varying Ar/O₂ flu ratio. The champion device had an efficiency of 3.87% with unintentional Cu-doping and back contact. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-Ray spectroscopy (EDS) were applied to study the properties of CdTe films. Before CdTe deposition, molybdenum oxide (MoO_x) was generated while heating the Mo substrate in an oxygen-containing environment. This buffer layer plays a pivotal role in blocking non-Ohmic back contact analyzed by current-voltage-temperature (J-V-T) measurements. Molybdenum oxidation states were extensively studied to build the relationship with a solar cell device. Our findings indicated that different oxygen partial pressure had less relevance with the CdTe surface chemical environment but was incredibly relevant for Mo metal foil oxidation states.